A series of balls appear to roll up hill. However, as you will quickly suspect, everything is not always what it appears to be. Once the camera moves to a different angle, the true shape of these ramps are revealed. Through an anamorphic trick in their design, the ramps appear to be angled upward when viewed from one vantage point. At all other angles, it is obvious that the ramps slope downward.
Brusspup created a template at http://i.imgur.com/D6nOq.jpg which you can download to construct your own impossible ramp. If you create your own ramp, please post links to image or videos of your version in the comments section.